A conventional image sensing apparatus such as a digital still camera performs a predetermined process on an electrical signal (image data) of a sensed image obtained by photoelectrically converting an optical image of an object with an image sensing device such as a CCD, and then records image information (image data) of the sensed image as electrical (magnetic) information on an external recording medium such as a memory card or a hard disk. Thus, unlike a conventional silver halide film camera which records an image on a film by exposing the film, the digital still camera applies image processes and records the electrical signal of the sensed image as positional information on pixels in one frame of the image so that the recorded image can be reproduced.
As for the digital still camera in recent years, high-pixelation of the image sensing device is underway for the sake of faithful reproduction of the image, and the quality of the reproduced image sensed by the digital still camera is becoming closer to the quality of the image sensed by the silver halide film camera.
However, there is a problem that a very large amount of information (data amount) is required as the image data of the sensed image to be recorded and reproduced in the digital still camera. Therefore, in general, a data amount of the sensed image to be recorded is reduced by compressing the image data before recording.
As for image compression methods for compressing the image data, there are a lossless compression method giving priority to preservability (reproducibility) at the sacrifice of compressibility and a lossy compression method giving priority to the compressibility at the sacrifice of the preservability (reproducibility). Concerning the lossless compression method, for instance, the method of developing differences between consecutive image data into run-length information and encoding it by using a table is generally known. As regards the lossy compression method, the method of suppressing high-frequency information of the image data by using orthogonal transformation such as discrete cosine transform (DCT) and then encoding it by using a table is generally known.
There are the cases, however, where a user using the digital still camera prefers selective use such as storing the image to be preserved merely as a record in the form of lossy-compressed image data and storing the image to be preserved as his/her work in the form of lossless-compressed image data. Furthermore, in conjunction with improved performance of the digital still camera, there are demands to generate the image data of the sensed image simultaneously by both the lossless compression method and lossy compression method.
Thus, there is a proposal of a digital camera capable of, without degrading a throughput in image sensing operation, compressing the image data of a sensed image by a plurality of different image compression methods and generating image data compressed by the respective image compression methods.
Both the lossless compression method and lossy compression method fall within the category of the conventional JPEG method. However, a JPEG image generally refers to the one compressed by the latter method. In general, the lossless-compress d image data is added with image developing conditions on generating the lossy-compressed JPEG image data.
The image processing conditions include the processing conditions in black correction, white balance correction, gray level correction and so on.
There is an image processing apparatus which receives the lossless-compressed image data and image developing conditions thus recorded and performs predetermined signal processing (developing processing) on the lossless-compressed image data using the image developing conditions. Such an image processing apparatus can generate an RGB image by changing the image developing conditions.
However, in the case where RGB image data is generated by developing the lossless-compressed image data using the changed image developing conditions used in the image sensing operation, the conventional image processing apparatus does not make any change to the JPEG image incidental to the lossless-compressed image data. To be more specific, if a new image development condition is set by the image processing apparatus, the image obtained from the lossless-compressed image data and the changed image developing conditions is different from the JPEG image incidental thereto (for instance, in brightness, color saturation, hue and so on).